Steady State Visually Evoked Potentials (SSVEP) are signals that are natural responses to visual stimulation

Stimulation

Stimulation is the action of various agents on nerves, muscles, or a sensory end organ, by which activity is evoked; especially, the nervous impulse produced by various agents on nerves, or a sensory end organ, by which the part connected with the nerve is thrown into a state of activity.The word...

 at specific frequencies

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

. When the retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

 is excited by a visual stimulus ranging from 3.5 Hz to 75 Hz, the brain generates electrical activity at the same (or multiples of) frequency of the visual stimulus.

This technique is used widely with electroencephalographic

EEG

EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...

 research regarding vision. SSVEP's are useful in research because of the excellent signal-to-noise ratio and relative immunity to artifacts. SSVEP's also provide a means to characterize preferred frequencies of neocortical dynamic processes. SSVEP is generated by stationary localized sources and distributed sources that exhibit characteristics of wave phenomena.